@ERROR: auth failed on module ... / password mismatch - Tools

This is a discussion on @ERROR: auth failed on module ... / password mismatch - Tools ; We have an odd situation where we have an rsyncd server running, that
generates a password mismatch error when access attempts are made from
some hosts, but not others.
rsync from host1 is as follows
rsync -vv user@server::STEREO
opening tcp ...